In general, since phosphorus (P) is present as an impurity in steel and degrades the quality of a steel product, for example, causes high temperature brittleness, the phosphorus (P) concentration in steel is preferably reduced except for a special case. Accordingly, a dephosphorization operation for removing phosphorus (P) in ferromanganese molten metal is performed.
In a typical dephosphorization operation for manufacturing ferromanganese, molten metal is charged into a ladle, an impeller is then dipped into the molten metal, and then the molten metal is stirred. Here, as illustrated in FIG. 12, a typical impeller 20 includes an impeller body 21 extending in the vertical direction, a plurality of blades 22 connected to a lower outer circumferential surface of the impeller body 21, blowing nozzles 23 formed to pass through each of the plurality of blades 22, a supply tube 24 formed to pass through the inner center of the impeller body 21 and the blades 22 and supplying a dephosphorization agent and gas to the blowing nozzles 23, and a flange 25 connected to the upper end of the impeller body 21. The flange 25 is also connected to a drive part (not shown) supplying rotational power.
A stirring flow according to the operation of this impeller 20 will be simply described as follows. As illustrated in FIG. 12, the stirring flow (solid arrow) generated by the rotation of the blades 22 is generated in the direction toward the inner wall of the ladle 10, collides then with the inner wall, and then flows to be separated into upward and downward directions along the inner wall of the ladle 10. However, a flow of the dephosphorization agent and the gas, which are discharged from the blowing nozzle 23, the flow ascending along the outer circumferences of the blades 22 and the impeller body 21, collides with a flow which collides with the inner wall of the ladle 10 by the rotation of the blades 22, then ascends, and then descends. Also, a flow of the dephosphorization agent and the gas, the flow ascending along the outer circumferences of the blades 22 and the impeller body 21, and descending then along the inner wall of the ladle 10, collides with a stirring flow which is generated by the rotation of the blades 22, and ascends along the inner wall of the ladle 10. Stirring force is cancelled by these collisions of the flows. Accordingly, the reaction rate between the molten metal and the dephosphorization agent is decreased and cause a decrease in a dephosphorization rate.
Thus, there are limitations in that it is not easy for an operator to remove phosphorus (P) up to a desired phosphorus concentration, and it takes a long time to remove phosphorus (P) up to a target value.
Also, there are limitations in that since a solid phase dephosphorization agent at room temperature is inputted into the molten metal, the temperature of the molten metal is decreased to thereby decrease a dephosphorization effect and a temperature-raising process to increase the temperature of the molten metal is required in a subsequent process.